How to promote polyhedral oligomeric silsesquioxanes (POSS) compatibility with polymers is always the key point of the research on POSS. Introduction of nitro groups into the POSS by nitration is an important method for improving the compatibility between POSS and other polymers. GPC, TGA, 1H NMR, FTIR and element analysis were used to characterize the structures of the products nitrated from cyclic ladder polyphenylsilsesquioxane (CL-PPSQ) by several kinds of nitration agents, including fuming nitric acid, HNO3-H2SO4, KNO3-H2SO4 and HNO3-(CH3CO)2O. The results showed that NO2-CL-PPSQ was prepared using 75% HNO3-(CH3CO)2O through a moderate nitration process, meanwhile the cyclic structure of PPSQ was remained, and NO2-CL-PPSQ of one nitryl group on every phenyl could be prepared. At the same time, the nitration mechanisms using different nitration reagents were analyzed. NO2+, which broke the chemical structure of CL-PPSQ, could be found in the fuming nitric acid and H2SO4-HNO3 (KNO3) systems. With regard to the HNO3-(CH3CO)2O system, the main activator was CH3COONO2 which had appropriate nitration ability. In brief, cyclic ladder polynitrophenylsilsesquioxanes have good solubility in organic solvent, good dispersion in the resin matrix and nitro groups with reaction activity at the same time. The successful synthesis of this polymer provides a precursor for subsequent amination, alkynyl, azide reaction.